In the field of superabsorbents, designated hereafter as SAP, cross-linked hydrophilic powdered polymers which are insoluble in water, based on free acrylic acid, partially or totally salified by an alkali metal are currently used.
These polymers are generally obtained by grinding polymer gels which have been chopped up and dried, these polymer gels being the product of a polymerization reaction in an aqueous solution of free acrylic acid, partially or totally salified by an alkali metal. It is known that these polymerization reactions in aqueous solution are carried out in a quasi adiabatic fashion starting with aqueous solutions with low monomer concentrations (about 10 to 25%) in such a manner as to be able to control the exothermic reaction. At the end of polymerization, polymer gels are obtained which are swollen with all the water used in the polymerization reaction and must be dried in order to be able to convert them into powder.
The handling of these water-swollen gels is laborious and delicate for they are soft and viscous, and their drying and then their grinding is more onerous the more water they contain.
In order to obviate these inconveniences, the Applicant has discovered new cross-linked, hydrophilic, powdered superabsorbents which are insoluble in water, based on silica and free acrylic acid polymers, partially or totally salified by an alkali metal.